U.S. patent application number 08/902954 was filed with the patent office on 2002-02-28 for rolling apparatus having surface-treated rolling member.
Invention is credited to HACHIYA, KOICHI, KINNO, DAI.
Application Number | 20020023695 08/902954 |
Document ID | / |
Family ID | 26481408 |
Filed Date | 2002-02-28 |
United States Patent
Application |
20020023695 |
Kind Code |
A1 |
KINNO, DAI ; et al. |
February 28, 2002 |
ROLLING APPARATUS HAVING SURFACE-TREATED ROLLING MEMBER
Abstract
Disclosed is a rolling apparatus having a surface-treated
rolling member composed of a metallic rolling element and a
metallic race element which have been used with a lubricant, in
which the surface of at least one of the rolling element and the
race element has a reaction product subsurface layer, wherein the
reaction product subsurface layer has been produced by the reaction
between the metallic component of the rolling element or the race
element and at least one compound selected from the group
consisting of a phosphorus compound, a sulfur compound, a halogen
compound and an organometallic compound, and the lubricant
containing at least one compound selected from the group consisting
of an organic phosphorus compound, an organic sulfur compound, an
organic halogen compound and an organometallic compound as an
extreme pressure component is present between the metallic contact
surfaces of the rolling member. The wettability of the metallic
surfaces in contact with each other by a lubricant is improved, and
the improved wettability by a lubricant is maintained so as to
improve resistance against seizure and wear. The rolling apparatus
exhibits improved resistance against seizure and wear, in which an
extreme pressure reaction film is previously formed on the metal
surface to improve the wettability of the metal surface by a
lubricant, and the wetting is maintained while running.
Inventors: |
KINNO, DAI; (KANAGAWA,
JP) ; HACHIYA, KOICHI; (KANAGAWA, JP) |
Correspondence
Address: |
SUGHRUE MION ZINN MACPEAK & SEAS
2100 PENNSYLVANIA AVENUE NW
WASHINGTON
DC
20037
|
Family ID: |
26481408 |
Appl. No.: |
08/902954 |
Filed: |
July 30, 1997 |
Current U.S.
Class: |
148/246 ;
106/14.26; 148/240; 148/271; 384/418 |
Current CPC
Class: |
F16C 33/30 20130101;
F16C 33/62 20130101; C10M 171/00 20130101 |
Class at
Publication: |
148/246 ;
148/240; 148/271; 384/418; 106/14.26 |
International
Class: |
C04B 009/02; C23C
022/00; F16C 035/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 30, 1996 |
JP |
8-200606 |
Jun 10, 1997 |
JP |
9-152503 |
Claims
What is claimed is:
1. A rolling apparatus having a surface-treated rolling member
composed of a metallic rolling element and a metallic race element
which have been used with a lubricant, in which the surface of at
least one of said rolling element and said race element has a
reaction product subsurface layer, wherein the reaction product
subsurface layer has been produced by the reaction between the
metallic component of said rolling element or said race element and
at least one compound selected from the group consisting of a
phosphorus compound, a sulfur compound, a halogen compound and an
organometallic compound, and said lubricant containing at least one
compound selected from the group consisting of an organic
phosphorus compound, an organic sulfur compound, an organic halogen
compound and an organometallic compound as an extreme pressure
component is present between the metallic contact surfaces of said
rolling member.
2. The rolling apparatus of claim 1, wherein the reaction product
subsurface layer has a thickness of 10 to 500 nm.
3. The rolling apparatus of claim 1, wherein the lubricant contains
the extreme pressure component in a concentration of 10 to 50,000
ppm, in terms of at least one of phosphorous, sulfur and
halogen.
4. The rolling apparatus of claim 1, wherein the lubricant contains
the extreme pressure component in a concentration of 10 to 10,000
ppm, in terms of at least one of phosphorous, sulfur and
halogen.
5. The rolling apparatus of claim 2, wherein the lubricant contains
the extreme pressure component in a concentration of 10 to 50,000
ppm, in terms of at least one of phosphorous, sulfur and
halogen.
6. The rolling apparatus of claim 2, wherein the lubricant contains
the extreme pressure component in a concentration of 10 to 10,000
ppm, in terms of at least one of phosphorous, sulfur and
halogen.
7. The rolling apparatus of claim 1, wherein the reaction product
subsurface layer is formed from a phosphorus compound and has a
thickness of 10 to 500 nm and the lubricant contains the extreme
pressure component in a concentration of 10 to 10,000 ppm, in terms
of at least one of phosphorous, sulfur and halogen.
8. The rolling apparatus of claim 1, wherein said compound selected
from the group consisting of a phosphorus compound, a sulfur
compound, a halogen compound, and an organometallic compound is
selected from the group consisting of phosphorous esters,
orthophosphoric esters, acidic phosphoric esters, sulfated fats and
oils, olefin sulfides, mercaptans, sulfides, sulfoxides, sulfones,
halogenated paraffins, halogenated fats and oils, metal
dihydrocarbyldithiophosphates, metal dihydrocarbyldithiocarbamates,
and metal naphthenates.
9. The rolling apparatus of claim 1, wherein the lubricant contains
at least one compound selected from the group consisting of
phosphoric esters, organometallic compounds, zinc dithiophosphate,
and organomolybdenum compounds as the extreme pressure
component.
10. The rolling apparatus of claim 1, wherein said reaction product
subsurface layer is formed by immersing the metallic rolling member
to be surface treated in a solution comprising an oil or organic
solvent and at least one compound selected from the group
consisting of an organic phosphorus compound, an organic sulfur
compound, an organic halogen compound and an organometallic
compound or coating the surface of the rolling member with the
solution, and thermally decomposing the compound(s) to carry out
the reaction.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a rolling apparatus having
a rolling member composed of a metallic rolling element and a
metallic race element, at least one of the rolling element and the
race element having been subjected to surface treatment for
improving resistance to seizure and wear. More particularly, it
relates to an improvement on lubricity in rolling apparatus, such
as rolling bearings, linear guide apparatus, and ball screw
apparatus.
BACKGROUND OF THE INVENTION
[0002] Lubrication of the above-mentioned rolling apparatus having
a rolling member is achieved with lubricants, such as oil and
grease. The lubricant serves to form an oil film on the surfaces of
the metallic rolling apparatus in contact with each other thereby
to reduce the friction on the contact surfaces and to improve wear
resistance. Under boundary lubrication in which a lubricating film
may possibly be broken, and metal surfaces can come into direct
contact with each other to cause solid friction or mixed friction,
an extreme pressure additive for improving resistance to wear and
seizure is added to the lubricant to prevent seizure and friction
between metal surfaces.
[0003] However, lubricants such as lubricating oil and grease
reduce their viscosity and consistency as temperature elevates as
is expressed in terms of viscosity index. Therefore, as temperature
increases, the film-forming function of the lubricant is reduced,
and it follows that the contact surfaces of the metallic rolling
member of a rolling apparatus come into the state of boundary
lubrication. Under boundary lubrication, the extreme pressure
additive added to the lubricant acts to prevent seizure through its
chemical reaction. The problem in this case is that the non-seizure
effect as expected cannot be obtained unless there is an outer
factor (e.g., heat) inducing the chemical reaction between the
extreme pressure additive and the metal surface.
SUMMARY OF THE INVENTION
[0004] The present invention has been completed taking a note of
the above-described problem of lubrication associated with
conventional rolling apparatus. Accordingly, an object of the
present invention is to provide a rolling apparatus having a
surface-treated rolling member exhibiting improved resistance
against seizure and wear, in which an extreme pressure reaction
film is previously formed on the metal surface to improve the
wettability of the metal surface by a lubricant, and the wetting is
maintained while running.
[0005] In order to accomplish the above object, the present
invention provides a rolling apparatus having a surface-treated
rolling member composed of a metallic rolling element and a
metallic race element which have been used with a lubricant, in
which the surface of at least one of the rolling element and the
race element has a film comprising a compound produced by the
reaction between the metallic component of the rolling element or
the race element therefor and at least one compound selected from
the group consisting of a phosphorus compound, a sulfur compound, a
halogen compound, and an organometallic compound (the film will
hereinafter be referred to as "reaction product subsurface layer"),
and a lubricant (oil or grease) containing at least one compound
selected from the group consisting of an organic phosphorus
compound, an organic sulfur compound, an organic halogen compound,
and an organometallic compound as an extreme pressure component is
present between the metallic contact surfaces of the rolling
member.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a cross section of a thrust bearing according to a
first embodiment of the present invention.
[0007] FIG. 2 is a cross section of a testing apparatus for
evaluating the first embodiment.
[0008] FIG. 3 is a graph showing the results of an evaluation test
on the first embodiment.
[0009] FIG. 4 is a perspective view of a linear guide apparatus
according to a second embodiment of the present invention.
[0010] FIG. 5 is a cross section of the second embodiment.
[0011] FIG. 6 is a graph showing the results of an evaluation test
on the second embodiment.
[0012] FIG. 7 is a graph showing the results of an evaluation test
on a third embodiment of the present invention.
[0013] FIG. 8 is a graph showing the results of an evaluation test
on a fourth embodiment of the present invention.
[0014] FIG. 9 is a graph showing the results of an evaluation test
on a fifth embodiment of the present invention.
[0015] FIG. 10 is a graph showing the results of an evaluation test
on a sixth embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The reaction product subsurface layer formed on the contact
surface makes the metallic surface more wettable by a lubricant,
thereby to accelerate the reaction of the surface with an extreme
pressure additive in the lubricant, which leads to improvement in
seizure resistance and wear resistance. Compared with an ordinary
metal surface, the metal surface having the reaction product
subsurface layer is more ready to enjoy the effects of an extreme
pressure additive on seizure and wear.
[0017] It is preferred that the reaction product subsurface layer
has a thickness of 10 to 500 nm and the lubricant contains the
extreme pressure component in a concentration of from 10 to 50,000
ppm, particularly from 10 to 10,000 ppm, in terms of at least one
of phosphorous, sulfur and halogen.
[0018] The reaction product subsurface layer can be formed by
immersing a metallic rolling member to be surface treated in a
solution comprising an oil or organic solvent and at least one
compound selected from the group consisting of a phosphorus
compound, a sulfur compound, a halogen compound and an
organometallic compound or coating the surface of the rolling
member with the solution, and thermally decomposing the compound(s)
to carry out the reaction. The thickness and surface roughness of
the reaction product subsurface layer can be controlled through
adjustments of the concentration of the compound(s) in the solution
or the reaction temperature and time.
[0019] The phosphorus compound which can be used to form a reaction
product subsurface layer (a phosphorus reaction product subsurface
layer) includes phosphorous esters, orthophosphoric esters, and
acid phosphoric esters. These compounds can be used either
individually or as a mixture of two or more thereof.
[0020] The sulfur compound which can be used to form a reaction
product subsurface layer (a sulfur reaction product subsurface
layer) includes sulfated fats and oils, olefin sulfides,
mercaptans, sulfides, sulfoxides, and sulfones. These compounds can
be used either individually or as a mixture of two or more
thereof.
[0021] The halogen compound which can be used to form a reaction
product subsurface layer (a halogen reaction product subsurface
layer) includes halogenated paraffins, halogenated fats and oils,
particularly chlorinated paraffins and chlorinated fats and oils.
These compounds can be used either individually or as a mixture of
two or more thereof.
[0022] The organometallic compound which can be used to form a
reaction product subsurface layer (an organometallic reaction
product subsurface layer) includes metal
dihydrocarbyldithiophosphates, metal dihydrocarbyldithiocarbamates,
and metal naphthenates.
[0023] The phosphorus compound, sulfur compound, and halogen
compound which can be used to form a reaction product subsurface
layer may be either organic or inorganic. Furthermore, the
compounds which can be used as an extreme pressure additive in the
present invention described below may be used to form a reaction
product subsurface layer.
[0024] The lubricant which can be used in the present invention can
be oil or grease to which at least one organic compound containing
at least one of phosphorus, sulfur, and halogen has been added as
an extreme pressure component. The extreme pressure additive added
to the lubricant as an extreme pressure component can be either a
polar compound or a non-polar compound as long as it is compatible
with the base oil of the lubricant. It is not particularly
necessary to consider matching between the reaction product
subsurface layer formed on the metal surface of a metallic rolling
member and the extreme pressure additive. Specific examples of
extreme pressure additives to be added to the base oil include
phosphoric esters, organometallic compounds, zinc dithiophosphate,
and organomolybdenum compounds, e.g., MoDTP and
Mo-dithiocarbamate.
[0025] The extreme pressure component is preferably added in such
an amount that the concentration of phosphorous, sulfur, or halogen
is 10 ppm or more, and the amount of the extreme pressure component
is preferably in the range of from 10 to 5000 ppm, more preferably
from 50 to 5000 ppm. If the concentration of the extreme pressure
component in a lubricant is less than 10 ppm, the reaction product
subsurface layer formed on the metal surface of the metallic
rolling member produces only slight effects in improving resistance
to seizure. If the concentration of the extreme pressure component
in a lubricant exceeds 5000 ppm, the lubricant tends to have poor
film-forming properties because of the excessive extreme pressure
component concentration. Accordingly, the upper limit of the
extreme pressure component concentration is preferably 5000 ppm,
while varying depending on the phosphorus, sulfur and/or halogen
content of the extreme pressure component.
[0026] According to the present invention, the metal surface of the
rolling member of a rolling apparatus is provided with improved
wettability by a lubricant by the formation of a reaction product
subsurface layer containing a phosphorus compound, a sulfur
compound, a halogen compound, an organometallic compound or a
combination thereof on the metal surface. As a result, the metal
surface is hardly exposed. Further, the extreme pressure component
present in the lubricant in a given concentration reacts with the
activated reaction product subsurface layer, whereby film formation
by the lubricant can be maintained. Thus, as compared with an
ordinary metal surface, the metal surface having the reaction
product subsurface layer enjoys the effects of the extreme pressure
additive on seizure and wear more easily to improve the resistance
to seizure and wear of the rolling apparatus.
[0027] The rolling apparatus according to the present invention can
be a rolling bearing (FIG. 1), in which case metallic rollers or
balls are equivalent to the "rolling element", and raceways on
which rolling elements roll are equivalent to the "race element",
the rollers or balls and the raceways constituting a rolling
member. The rolling apparatus of the present invention can also be
a linear guide apparatus (FIG. 4), in which case metallic rollers
or balls are equivalent to the "rolling element", and rolling
grooves of the guide rail on which the rolling elements roll are
equivalent to the "race element", the roller or balls and the
rolling grooves constituting a rolling member.
[0028] The embodiments for carrying out the present invention will
be described with reference to the accompanying drawings.
(I) First Embodiment
[0029] FIG. 1 is a cross section of a first embodiment in which the
present invention is applied to a thrust bearing having a rolling
member composed of metallic rolling elements and race elements
therefor to improve resistance to seizure.
[0030] The thrust bearing 1 shown in FIG. 1 is a cageless ball type
rolling member comprising upper and lower races 2 and 3 as race
elements and balls 5 as rolling elements rolling on these race
elements. The upper and lower races 2 and 3 of the thrust bearing 1
were surface-treated according to the present invention to form a
reaction product subsurface layer. The bearing was combined with a
lubricating oil containing an extreme pressure additive and
subjected to a seizure test.
[0031] (1) Preparation of Samples
[0032] The surface (raceway) 4 of the races 2 and 3 of a thrust
bearing 1 was cleaned with petroleum benzine and immersed in
synthetic oil containing 10% by weight of dibutyl sulfide at
160.degree. C. for 10 hours to form a 40 nm thick sulfur reaction
product subsurface layer on the raceway 4.
[0033] The thickness of the reaction product subsurface layer was
measured with an X-ray photoelectron spectrophotometer (XPS).
Measurement with XPS is carried out by irradiating a sample with
X-rays and analyzing the energy of photoelectrons emitted from the
outermost surface (about several angstroms deep) of the sample to
get qualitative and quantitative information about the elements on
the sample surface and the state of bonding of the elements. It is
also possible to analyze the distribution of the elements in the
thickness direction by making the measurement with XPS while
sputtering (etching) the surface with an argon (Ar) ion gun. For
example, in measuring the thickness of a reaction product
subsurface layer formed by using an organic sulfur compound, the
depth profile of a sample is obtained with XPS while sputtering
with an argon ion gun at a constant etching rate (e.g., 3 nm/min).
The depth immediately before the point at which the photoelectron
intensity assigned to sulfur in the reaction product subsurface
layer comes to show no change is taken as the thickness of the
film.
[0034] It should be noted that the reaction product subsurface
layer is not a layer laminated on the surface of a sample (matrix)
but a layer integral with the matrix which is formed from the
surface toward the inside on chemical reaction of the matrix. In
other words, unlike a layer merely laminated on the surface of the
matrix, the reaction product subsurface layer is hardly separated.
Therefore, measurement of film thickness (i.e., depth from the
matrix surface) needs sputtering with an ion gun as noted
above.
[0035] (2) Seizure Resistance Test
[0036] The seizure resistance of the surface-treated thrust bearing
1 was evaluated.
[0037] As shown in FIG. 2, the upper and lower races 2 and 3 of the
thrust bearing 1 were fitted to a vertical spindle 6, and the
spindle was revolved at 7000 rpm with a thrust load Fa of 400 kgf
applied as indicated with an arrow. The thrust bearing 1 had
previously been lubricated by dropping 3 .mu.l of spindle oil onto
the rolling elements 5 and raceways 4 by means of a microsyringe. A
plurality of spindle oil species containing a varied amount of
n-butylmercaptan were prepared as a lubricant, and a plurality of
seizure resistance tests were carried out using each of the
lubricants. The time from the start of revolution to development of
seizure was measured. The time when the reading of a thermocouple
inserted in the lower lace 3 got out of the equilibrium state at
100.degree. C. or lower and exceeded 200.degree. C. was taken as a
seizure time.
[0038] The duration before development of seizure is shown in FIG.
3, in which the results of the surface-treated thrust bearing and
the untreated thrust bearing are plotted as -.diamond.- and
-.box-solid.-, respectively. It is apparent from the test results
that the combination of the surfaces 4 of the races 2 and 3 of the
bearing 1 having formed thereon a sulfur-containing reaction
product subsurface layer and the organic sulfur compound-containing
extreme pressure additive shows greatly improved seizure resistance
over a broad range of the extreme pressure component concentration
as compared with a combination of an untreated bearing and the same
extreme pressure additive.
[0039] The thickness of the reaction product subsurface layer used
in this embodiment is not particularly limited and can be selected
arbitrarily by controlling the surface treatment conditions as far
as the surface roughness is not adversely affected.
[0040] A suitable concentration of the extreme pressure component
(sulfur in this embodiment) ranges from 10 to 50000 ppm. A
concentration ranging from 100 to 10000 ppm is especially effective
on prevention of seizure. If the concentration is less than 10 ppm,
the effect in improving resistance to seizure is small. If it
exceeds 50000 ppm, the lubricating effect of the base oil of the
lubricant is lessened, failing to obtain improvements in
performance.
(II) Second Embodiment
[0041] The second embodiment of the present invention will be
illustrated.
[0042] FIG. 4 is a perspective general view of a linear guide
apparatus as another embodiment of the rolling member having
metallic rolling elements and race elements therefor, and FIG. 5
shows its cross section.
[0043] The linear guide apparatus 10 comprises a metallic guide
rail 11 having rolling grooves 12 as race elements on its either
side, a number of rolling elements 13 that roll on the rolling
grooves 12, and a slider 14 that is fitted onto the guide rail 11
via the rolling elements 13. In the slider 14 there is a
circulation passage for rolling elements which is composed of
through-holes 15 made in the axial direction and a U-shaped passage
made through end cap 16 provided on each end of the slider. The
slider 14 slides both ways along the guide rail 11 with the rolling
elements 13 circulating through the circulation passage. Numeral 17
is a plastic ball retainer.
[0044] (1) Preparation of Samples
[0045] In this embodiment, a reaction product subsurface layer
having a thickness of 50 nm was formed on the surface of rolling
elements 13 by immersing the rolling elements 13 in a 5 wt %
solution of dilauryl hydrogenphosphite in a synthetic hydrocarbon
solvent at 110.degree. C. for 4 hours. The thus treated rolling
elements 13 were set in a slider 14, and the slider with the
rolling elements was fitted onto a guide rail 11 to assemble a
linear guide apparatus 10.
[0046] (2) Wear Resistance Test
[0047] The wear resistance of the resulting surface-treated linear
guide apparatus 10 was evaluated as follows.
[0048] The vacant space of the slider 14 of the linear guide
apparatus 10 was filled with 1 g of commercially available grease
to which an extreme pressure additive had been added. The slider 14
was made to slide two ways along the guide rail 11 over a total
distance of 500 km under an applied load of 200 kgf by adjusting
the diameter of the rolling elements (balls) 13. Thereafter the
wear (.mu.m) of the rolling grooves 12 of the guide rail 11 was
measured.
[0049] Trioctyl phosphite was chosen as an extreme pressure
additive added to the grease. The above test was repeatedly carried
out under the same conditions but using grease containing the
extreme pressure additive in a varied phosphorus concentration to
measure the wear of the rolling grooves 12. The results obtained
are shown in FIG. 6, in which the results of the surface-treated
thrust bearing and the untreated thrust bearing are plotted as
-.diamond.- and -.box-solid.-, respectively.
[0050] As can be seen from the test results, a preferred content of
the extreme pressure component (phosphorus in this particularly
embodiment) in grease ranges from 10 to 20000 ppm, and a range of
from 100 to 5000 ppm is particularly effective in improving wear
resistance. If the phosphorus content is less than 10 ppm, the wear
improving effect is small. A phosphorus content exceeding 20000 ppm
adversely affects the lubricating performance of the base oil of
the grease, and no improvements in wear resistance is expected.
[0051] It is apparent from this embodiment that the combination of
the phosphorus-containing reaction product subsurface layer and an
organic phosphorus compound, which is an extreme pressure additive
added to grease, produces a considerable effect in improving wear
resistance.
(III) Third Embodiment
[0052] A single row deep groove ball bearing (JIS: 6206) as a
sample was set on the testing apparatus shown in FIG. 2
horizontally and subjected to a revolution test. That is, either
the balls or the inner race of the ball bearing was surface treated
to form a reaction product subsurface layer, combined with a
lubricating oil containing an extreme pressure additive, and
subjected to a seizure resistance test. The results obtained were
compared with those of Comparative Examples.
[0053] (1) Preparation of Samples
[0054] The balls or inner race of a ball bearing was immersed in a
4 wt % solution of TCP (tricresyl phosphate) in a synthetic
hydrocarbon solvent at 180.degree. C. for 40 hours to cause thermal
decomposition thereby to form a 0.2 .mu.m thick reaction product
subsurface layer on the surface of the sample.
[0055] (2) Seizure Resistance Test
[0056] The seizure resistance of the resulting surface-treated ball
bearing was evaluated.
[0057] The seizure resistance test was carried out by horizontally
fitting the ball bearing to a vertical spindle 6 and revolving the
spindle at 6000 rpm with a thrust load Fa of 400 kgf applied as
shown in FIG. 2. Mineral oil-based grease to which MoDTC
(molybdenum dithiocarbamate) had been added as an extreme pressure
additive in an amount varying up to 10000 ppm in terms of sulfur
concentration was used as a lubricant for the ball bearing. The
site of the ball bearing which was subjected to the surface
treatment and the content of the extreme pressure additive in the
lubricant (grease) are shown in Table 1 below.
1 TABLE 1 Extreme Site of Pressure Surface Additive Lubricant
Treatment Content (ppm) Comparative grease balls 0 Example 3-1
Comparative grease + MoDTC -- 10-10000 Example 3-2 Example 3-1
grease + MoDTC balls 10-10000 Example 3-2 grease + MoDTC inner race
10-10000
[0058] The relationship of duration up to seizure development
(hour) vs. concentration of the additive (S concentration: ppm) is
shown in FIG. 7, in which the curves indicated by C3-1, C3-2, E3-1,
and E3-2 correspond to the results of Comparative Examples 3-1 and
3-2, and Examples 3-1 and 3-2, respectively.
[0059] Comparison of the durability test results between
Comparative Example 3-1 and Example 3-1 reveals the synergistic
effect of the combination of the surface treatment according to the
present invention and an extreme pressure additive present in a
lubricant in extending the life of a bearing.
[0060] Comparison between Comparative Example 3-2 and Examples 3-1
and 3-2 proves the effect of the surface treatment according to the
present invention in lubrication using an extreme pressure
additive-containing lubricant.
[0061] It is understood from FIG. 7 that the effective
concentration of an extreme pressure additive in a lubricant
preferably ranges from 10 to 2000 ppm, particularly from 10 to 1500
ppm, in terms of sulfur concentration.
[0062] It should be noted that the above-specified concentration
range is by no means limiting and is subject to variation depending
on the sulfur ratio in the organic sulfur compound used as an
extreme pressure additive.
(IV) Fourth Embodiment
[0063] Samples were prepared by surface treating the same ball
bearing as used in the third embodiment while altering the
conditions of thermal decomposition, i.e., the reaction temperature
and time, to form a reaction product subsurface layer having a
thickness (depth) varying from 0.003 to 0.6 .mu.m (=3 to 600 nm).
The resulting samples were subjected to a seizure resistance test
in the same manner as described above to examine the influence of
the film thickness on the durability of the bearing.
[0064] The site of the heat treatment and the depth of the formed
reaction product subsurface layer are shown in Table 2 below.
2 TABLE 2 Reaction Site of Product Surface Subsurface Lubricant
Treatment Layer (nm) Comparative grease + MoDTC -- 0 Example 4
Example 4-1 grease + MoDTC rolling 10-500 elements Example 4-2
grease + MoDTC inner race 10-500
[0065] Mineral oil-based grease containing 500 ppm, in terms of
sulfur, of MoDTC as an extreme pressure component was used for
lubrication of the ball bearing.
[0066] The relationship of durability up to development of seizure
(hour) vs. depth (nm) of the reaction product subsurface layer is
plotted in FIG. 8, in which the curves indicated by E4-1, E4-2, and
C4-1 correspond to the results of Examples 4-1, 4-2 and Comparative
Example 4-1, respectively. Comparison between Comparative Example
4-1 and Examples 4-1 and 4-2 provides confirmation to the effect of
the surface treatment according to the present invention. It is
seen that the effective depth of the reaction product subsurface
layer formed by the surface treatment ranges from 10 to 500 nm,
preferably from 30 to 300 nm, still preferably from 30 to 200 nm,
and particularly preferably from 50 to 100 nm.
[0067] It is apparently revealed from the results of the third and
fourth embodiments that the wear improving effect obtained from a
combination of a phosphorus-containing reaction product subsurface
layer and a lubricant containing an organic sulfur compound as an
extreme pressure additive is significant equally to the effects
produced from the combination of the first embodiment (a sulfur
compound-containing reaction product subsurface layer+sulfur
additive-containing lubricant) or the second embodiment (a
phosphorus compound-containing reaction product subsurface
layer+phosphorus additive-containing lubricant).
[0068] Effective extreme pressure additives that can be added to
the lubricant for use in the present invention include, in addition
to the above-described examples, organometallic sulfur compounds,
organometallic phosphorus compounds, organometallic chlorine
compounds, metal-free organic sulfur compounds, organic phosphorus
compounds, and organic chlorine compounds. Some of these compounds
contain nitrogen, oxygen, etc. as a constituent element.
Commercially available lubricants generally contain phosphorus (P)
type and sulfur (S) type additives in combination. Therefore, the
reaction product subsurface layer according to the present
invention can be used effectively in combination with these
commercially available lubricants, either of phosphorus type or
sulfur type.
(V) Fifth Embodiment
[0069] The present invention was applied to a ball bearing for the
main shaft of a supercharger, and the bearing was tested under a
non-oiling condition.
[0070] All the rolling elements (balls) and the outer and inner
races of the ball bearing were surface treated in accordance with
the present invention to have a reaction product subsurface layer.
A combination of the surface treated bearing and a lubricating oil
containing an extreme pressure additive was subjected to a seizure
resistance test, and the results obtained were compared with those
of Comparative Example.
[0071] (1) Preparation of Samples
[0072] The ball bearing for the main shaft of a supercharger used
here is a three-point contact ball bearing having an inner diameter
of 42 mm and an outer diameter of 86 mm, the inner race of which is
divided into two. The sample of Example was prepared by immersing
the balls and the outer and inner races in a 5 wt % solution of TCP
in a synthetic hydrocarbon oil at 200.degree. C. for 50 hours to
induce thermal decomposition reaction thereby to form a reaction
product subsurface layer containing both phosphorus and oxygen and
having a practically uniform thickness (depth) of 100 to 120 nm on
the surface. The sample of Comparative Example was prepared by
immersing the balls and the inner and outer races in a synthetic
hydrocarbon containing less than 10 ppm of TCP at 200.degree. C.
for 50 hours.
[0073] (2) Seizure Resistance Test
[0074] The resulting surface-treated ball bearings were tested to
evaluate the resistance to seizure.
[0075] A non-oiling test was carried out as follows using gas
turbine oil meeting MILL-23699 (the U.S. Air Force Specifications)
as a lubricant for the ball bearing. The phosphorus concentration
of a phosphorus type extreme pressure additive in the lubricant was
varied by adjusting with TCP. After revolving the bearing at 50000
rpm while oiling at a rate of 3 l/min, the oiling was stopped, and
the bearing was run for an additional 10 minutes while measuring
the temperature of the bearing. Thereafter, the bearing was taken
apart, and each member was inspected. After the stop of oiling, the
temperature of the bearing increased. As for those samples whose
heat was dissipated without reaching to a constant temperature, the
time for reaching the dissipation state, taken as a duration, was
plotted against the phosphorus concentration of the lubricant.
[0076] The site of the surface treatment of the bearing and the
extreme pressure additive content in the lubricant (oil) are shown
in Table 3 below.
3 TABLE 3 Content of Site of Surface Extreme Pressure Lubricant
Treatment Additive (ppm) Comparative Oil balls and inner 0 Example
5 (Henkel and outer races 2939) Example 5 Oil + TCP balls and inner
10-10000 and outer races
[0077] The relationship between duration (second) and concentration
of the additive (P; ppm) is shown in FIG. 9, in which the curves
indicated by E5 and C5 correspond to the results of Comparative
Example 5 and Example 5, respectively.
[0078] From the test results of Example 5 compared with Comparative
Example 5 (FIG. 9) it is seen that the effect on durability
improvement is produced at a phosphorus concentration, originated
in TCP, of 10 ppm or higher in gas turbine oil. At lower P
concentrations, the effect of the additive is low. If the P
concentration exceeds 10000 ppm, there will arise the problem of
corrosion due to the water content in the oil. Accordingly, the
phosphorus concentration in the lubricant is preferably 10 to 10000
ppm, still preferably 100 to 10000 ppm, particularly preferably 200
to 5000 ppm.
[0079] The phosphorus concentrations in commercially available gas
turbine oil are, for example, 2000 to 5000 ppm in Mobile Jet Oil 2
and Mobile Jet Oil 2254; 400 ppm or more in Aeroshell Turbine Oil
555 and 560; 100 ppm or more in Exxon Turbo Oil 25; and 1500 ppm or
more in Exxon Turbo Oil 238. Namely, any of these products has a
phosphorus concentration falling within the effective range as
specified in the present invention and is therefore adequate for
the purpose of obtaining satisfactory durability in cooperation
with the reaction product subsurface layer of the present
invention.
[0080] Other commercially available lubricating oils and grease
inclusive of those already containing at least one of organic
phosphorus compounds, organic sulfur compounds, organic halogen
compounds, and organometallic compounds as an extreme pressure
additive are also suited as a lubricant to be used in the present
invention. Examples of lubricants applicable to the present
invention include commercially available turbine oil, gasoline
engine oil, diesel engine oil, 2-cycle engine oil, racing engine
oil, automatic transmission oil, gear oil, hypoid gear oil, and
spindle oil. More specifically, examples of useful turbine oil,
typified by gas turbine oil, are Mobile Jet Oil 254, Mobile Jet Oil
2, Aeroshell Turbine Oil 308, 390, 500, 555, 560 and 750, and Exxon
Turbo Oil 2380, 25, 274, 85, 2389, and 390. Other useful oil and
grease include those available from Exxon Chemical Corp., Esso
Sekiyu K.K., NOK Kluber K.K., Kygnus Sekiyu K.K., Idemitsu Kosan
Co., Ltd., Kyushu Oil Company, Limited., Kyodo Oil Co., Ltd., Kyodo
Yushi Co., Ltd., Cosmo Oil Co., Ltd., San-Ai Oil Co., Ltd., Japan
Energy K.K., Showa Shell Sekiyu Kabushiki Kaisha, Nippon Steel
Chemical Co., Ltd., Dow Corning Corp., Nippon Grease K.K., Nippon
Oil Company, Ltd., Fuji Kosan K.K., Mitsui Petrochemical
Industries, Ltd., Matsumura Sekiyu K.K., Mitsubishi Oil Co., Ltd.,
Mobil Sekiyu K.K., and Yushiro Chemical Ind. Co., Ltd. The brands
and manufacturers are not limited to the above-enumerated
examples.
(VI) Sixth Embodiment
[0081] The same bearing for the main shaft of a supercharger as
used in the fifth embodiment was used. A reaction product
subsurface layer was formed to a varied depth while fixing the
phosphorus concentration of a lubricant at 3000 ppm. The resulting
surface treated bearings were tested for seizure resistance under a
non-oiling condition in the same manner as described above.
[0082] The depth of the reaction product subsurface layer was
controlled in a range of from 10 to 1000 nm by adjusting the
reaction temperature and time. The samples were subjected to a
seizure resistance test to examine the influence of the depth of a
reaction product subsurface layer upon the life of a bearing. The
lubricant used, the site of surface treatment conducted, and the
depth of the formed reaction product subsurface layer are shown in
Table 4 below.
4 TABLE 4 Depth of P Reaction Site of Product Surface Subsurface
Lubricant Treatment Layer (nm) Comparative Oil + TCP -- -- Example
6 Example 6 Oil + TCP balls and 10-1000 outer and inner races
[0083] A lubricating oil containing TCP (P concentration: 3000 ppm)
was used as a lubricant.
[0084] The relationship between depth (nm) of the reaction product
subsurface layer and duration up to development of seizure (second)
is shown in FIG. 10, in which the curves indicated by C6 and E6
correspond to the results of Comparative Example 6 and Example 6,
respectively. Example 6 shown in FIG. 10 provides confirmation of
the effect of the surface treatment according to the present
invention. If the depth of the reaction product subsurface layer is
less than 30 nm, the durability is poor. The depth is preferably 30
to 600 nm, still preferably 50 to 500 nm, particularly preferably
80 to 300 nm. If it exceeds 600 nm, the surface profile is
deteriorated to reduce the durability improving effect.
[0085] Where commercially available oil, Mobile Jet Oil 2 or 254,
was used in the above embodiment, the bearing had a durability of
600 sec. or longer when the reaction product subsurface layer had a
thickness of 50 to 500 nm.
[0086] The reaction product subsurface layer in the above-described
embodiments can also be formed by immersion under heat using
commercially available gas turbine oil listed above as examples of
useful lubricants.
[0087] While in the foregoing embodiments, the present invention
has been described by referring to a rolling bearing as a rolling
apparatus having a rolling member comprising a rolling element made
of metal and its race element, the present invention is not
construed as being limited to these embodiments. That is, the
present invention is applicable to other rolling apparatus, such as
a linear guide apparatus and a ball screw apparatus, as well. In
the case of a ball screw apparatus, the metallic balls correspond
to the "rolling element", and the screw channel on the ball screw
axis to the "race element" for the rolling element, the balls and
the ball screw axis constituting a "rolling member".
[0088] As described above, according to the present invention, a
reaction product subsurface layer containing phosphorus, sulfur or
halogen which is formed on the surface of the metallic rolling
member of a rolling apparatus functions to improve the wettability
of the surface of the metallic member by a lubricant. In addition,
an extreme pressure component incorporated into a lubricant reacts
with the activated reaction product subsurface layer to bring about
improvements in resistance to seizure and wear of the rolling
member over the conventional lubrication systems.
[0089] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made therein without departing from the spirit and scope
thereof.
* * * * *